Baryons and baryonium in QCD2

The light particle spectrum of quantum chromodynamics in (1 + 1) dimensions is considered for the limit of strong coupling (g ? m), where g is the coupling constant and m is the bare mass of the fermions. The spectrum is shown to be composed of baryons and baryon-antibaryon bound states. The spectrum is computed to lowest order in m/g and the results are compared with those of other treatments of QCD₂.     

Electromagnetic mixing of narrow baryonium states

We discuss the theoretical possibility that electromagnetic mixing in the recently discovered narrow baryon-antibaryon resonances might be comparable to quark configuration mixing, because of the expected smallness of OZI rule violations of those masses. Nearly “pure” quark states could result. This phenomenon could reveal itself in large violations of isospin and G parity at a single peak and could explain the absence of the S(1936) in $\text{p}$p → $\text{n}$n. It should manifest itself most clearly in $\text{p}$n and $\text{n}$p scattering.     

A model for baryonium

The spectrum of $\text{qq}\text{q}\text{q}$ hadrons examined in a quark-gluon model yields two types of state both of which have small mesonic widths and may be associated with baryoniums. One type (T-diquonium) has normal hadronic widths into $\text{B}\text{B}$, while other (M-diquonium) is narrow and decays into $\text{B}\text{B}$ only reluctantly, preferring if possible to decay by cascade. The experience gained from ordinary hadron spectroscopy, plus some new phenomenological observations, allow one to predict the spectrum and properties of both types in considerable detail. The result bears close resemblance to present experiment.The existence of narrow M-diquonium states follows only from hidden colour, and if established would be a major triumph for the concept. It would be, however, only the first example of a quite general phenomenon which may well develop into a whole new branch of hadron spectroscopy.     

Small quarkonium states in an anisotropic QCD plasma

We determine the hard-loop resummed propagator in an anisotropic QCD plasma in general covariant gauges and define a potential between heavy quarks from the Fourier transform of its static limit. We find that the potential exhibits angular dependence and that binding of very small quarkonium states is stronger than in an isotropic plasma.     

Analysis of the X(1835) and related baryonium states with Bethe-Salpeter equation

In this article, we study the mass spectrum of the baryon-antibaryon bound states p [`(p)] \bar{{p}} , S \Sigma [`(S)] \bar{{\Sigma}} , X \Xi [`(X)] \bar{{\Xi}} , L \Lambda [`(L)] \bar{{\Lambda}} , p [`(N)] \bar{{N}}(1440) , S \Sigma [`(S)] \bar{{\Sigma}}(1660) , X \Xi [`(X)]<sup>￠</sup> \bar{{\Xi}}^{{\prime}}_{} and L \Lambda [`(L)] \bar{{\Lambda}}(1600) with the Bethe-Salpeter equation. The numerical results indicate that the p [`(p)] \bar{{p}} , S \Sigma [`(S)] \bar{{\Sigma}} , X \Xi [`(X)] \bar{{\Xi}} , p [`(N)] \bar{{N}}(1440) , S \Sigma [`(S)] \bar{{\Sigma}}(1660) , X \Xi [`(X)]^￠ \bar{{\Xi}}^{{\prime}}_{} bound states maybe exist, and the new resonances X(1835) and X(2370) can be tentatively identified as the p [`(p)] \bar{{p}} and p [`(N)] \bar{{N}}(1440) (or N(1400)[`(p)] \bar{{p}} bound states, respectively, with some gluon constituents, and the new resonance X(2120) may be a pseudoscalar glueball. On the other hand, the Regge trajectory favors identifying the X(1835) , X(2120) and X(2370) as the excited h^￠ \eta^{{\prime}}_{}(958) mesons with the radial quantum numbers n = 3 , 4 and 5, respectively.     

Light four-quark states and QCD sum rule

The relations among four-quark states, diquarks and QCD sum rules are discussed. The situation of the existing, but incomplete studies of four-quark states with QCD sum rules is analyzed. Masses of some diquark clusters were attempted to be determined by QCD sum rules, and masses of some light tetraquark states were obtained in terms of the diquarks.     

Light four-quark states and QCD sum rule

The relations among four-quark states, diquarks and QCD sum rules are discussed. The situation of the existing, but incomplete studies of four-quark states with QCD sum rules is analyzed. Masses of some diquark clusters were attempted to be determined by QCD sum rules, and masses of some light tetraquark states were obtained in terms of the diquarks.     

An infrared-stable multiplicity measure on QCD parton states

We suggest a measure of multiplicity in e⁺e⁻ annihilation events which is based upon a generalization of the available phase phase in two-jet events to multi-gluon events. This measure exhibits infrared stability, the anomalous dimensions found in perturbative QCD, together with an intermittent behaviour. Well defined expressions can be obtained not only asymptotically but for all energies.     

Dual amplitudes of baryonium interaction

It is shown that the interaction of the M₀^J-baryonium can be described by Brower-Goddard dual amplitudes with n=3, where n is the dimension of “Koba-Nielsen” variables.     

Narrow states in38,40Ar via alpha +34,36S scattering

Excitation functions of the elastic scattering α+ ^34,36 S has been measured at beam energies E _α =12.56–15.00 MeV. Strongly fluctuating large cross sections in backward angles have been observed. Angular distributions were measured in the range θ _lab =98°–173° for fourteen energies, and many of them turned out to be dominated by one exclusive angular-momentum value, a behaviour typical for resonance scattering.     

Quark-antiquark bound states and QCD running coupling within infrared confinement

Bound states of spin-half and spin-one particles are studied within a relativistic quantum-field model based on the infrared confinement. The spectra of quark-antiquark and two-gluon states are determined by master equations similar to the ladder Bethe-Salpeter equations. Masses of light, intermediate and heavy mesons are estimated in a wide range of scale (from hundreds MeV up to 10 GeV). A new, independent and specific infrared-finite behavior of QCD effective coupling is revealed in the low-energy domain.     

Excited states of light hadrons as a probe of QCD

The dynamics of light hadrons being highly sensitive to the confinement force, it is suggested that a careful study of the excitation pattern of light hadrons might be the most effective way to unravel the mechanisms of confinement dynamics. As a case study, it is shown how the recently confirmed doubling of the ρ' (1600) (which in potential models relies on an accidental level degeneracy) finds a simple interpretation in the framework of a string picture for flux-tube dynamics.